This study will examine the specificity and significance of retrograde axoplasmic transport to the visual system, using biochemical and light and electron microscopic cytochemistry. Purified isoenzymes of horseradish peroxidase will be modified chemically and tested in vivo to determine which groups on this molecule are required for its uptake and retrograde transport by axons of retinal ganglion cells and neurons of the lateral geniculate nucleus. The metabolism of phospholipids in the vertebrate retina will be studied after exposure to different neurotransmitters and light and dark adaptation, using biochemical, light and electron microscopic radioautography, and fluorescence microscopy techniques. Studies on the development of the retina and visual system of the albino rat will be continued, using light microscopy radioautography for H3-thymidine studies, combined H3-thymidine and horseradish peroxidase neuronography, Golgi techniques and fluorescence microscopy. A new neuroanatomical tracing technique will be developed, based on retrograde axoplasmic transport for demonstration of axonal collaterals in the visual system after normal and aberrant development.